overhad / housekeeping

OK somewhat useless knowledge question. What is in the overhead / housekeeping portion of the SLC 500 processors? I know it checks the watchdog for a time out becauseof a hang up. But what else is in there?

See pdf bellow

Hi Jeff ...

here's a couple more for your scrapbook ...

(1) check for the Math Overflow Flag bit S:5/0 ...

(2) communicate with the programming terminal, HMI, etc. ... check out the SVC instruction for more trivial information along those lines - and then apply that approach to my YouTube Lesson #9 - starting at time 5:45 - and especially at time 6:30 ...

may be able to add more later ... got things to do ...

PS EDIT ... well, I see Mickey is "up and at 'em" already this morning ...

Something to think about

JeffKiper said:

OK somewhat useless knowledge question. What is in the overhead / housekeeping portion of the SLC 500 processors? I know it checks the watchdog for a time out becauseof a hang up. But what else is in there?

Click to expand...

If the program 'hangs up' how does it finish the scan?

The overhead section probably does a lot of communication things. For instance the state of the items that are being monitored is saved to be sent to RS500.

There must be some clean up of unused ladders during the over head period. When doing on-line editing the new rung must be added and eventually the old rung must be deleted. There may be some 'garbage' collection going on.